Field emission display having matrix material

ABSTRACT

A black matrix material for increasing resolution and contrast of field emission displays is disclosed. The black matrix material is preferably deposited by electrophoresis in the interstitial regions between phosphor pixels of the faceplate. By this technique, high resolution and/or small surface area field emission displays may be manufactured. The black matrix material does not brown when subjected to the conditions associated with the manufacture of field emission displays, is chemically inert and remains stable under vacuum conditions and electron bombardment. The black matrix material is selected from boron carbide, silicon carbide, tungsten carbide, vanadium carbide and mixtures thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of pending U.S. patent applicationSer. No. 09/541,352, filed Mar. 31, 2000, now U.S. Pat. No. 6,224,730,which is a divisional of pending U.S. patent application Ser. No.09/234,087, filed Jan. 19, 1999, now U.S. Pat. No. 6,296,750, which is adivisional of U.S. patent application Ser. No. 08/835,295, filed Apr. 7,1997, issued Sep. 12, 2000, as U.S. Pat. No. 6,117,294, which is acontinuation-in-part of U.S. patent application Ser. No. 08/589,039,filed Jan. 19, 1996, issued Jun. 9, 1998, as U.S. Pat. No. 5,762,773.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Contract No.DABT63-93-C-0025 awarded by the Advanced Research Projects Agency(ARPA). The Government has certain rights in this invention.

TECHNICAL FIELD

This invention relates to the art of manufacture of field emissiondisplays, and in a specific application, to the fabrication of patternedphosphor screens for high resolution displays. More specifically, thepresent invention relates to a black matrix material for such displays,and to a black matrix material which adheres to the interstitial regionsbetween light-emitting phosphor pixels of a field emission display.

BACKGROUND OF THE INVENTION

Many devices, such as computers and televisions, require the use of adisplay screen. Some of these devices, such as laptop computers, requirea lightweight, portable screen as a display screen. Currently, suchscreens typically use electroluminescent or liquid crystal displaytechnology. A promising technology to replace these types of screens isthe field emission display (FED).

Field emission displays typically include a generally planar substratehaving an array of projecting emitters. In many cases, the emitters areconical projections integral to the substrate. Typically, the emittersare grouped into emitter sets where the bases of the emitters in eachset are commonly connected.

A conductive extraction grid is positioned above the emitters and drivenwith a voltage of about 30-120 V. The emitter sets are then selectivelyactivated by providing a current path from the bases to the ground.Providing a current path to ground allows electrons to flow from theemitters in response to the extraction grid voltage. If the voltagedifferential between the emitters and extraction grid is sufficientlyhigh, the resulting electric field extracts electrons from the emitters.

Field emission displays also include display screens mounted adjacentthe substrates. The display screens are formed from glass plates coatedwith a transparent conductive material to form an anode biased to about1-2 kV. A cathodoluminescent layer covers the exposed surface of theanode. The emitted electrons are attracted by the anode and strike thecathodoluminescent layer, causing the cathodoluminescent layer to emitlight at the impact site. The emitted light then passes through theanode and the glass plate where it is visible to a viewer.

The brightness of the light produced in response to the emittedelectrons depends, in part, upon the rate at which electrons strike thecathodoluminescent layer, which in turn depends upon the magnitude ofcurrent flow to the emitters. The brightness of each area can thus becontrolled by controlling the current flow to the respective emitterset. By selectively controlling the current flow to the emitter sets,the light from each area of the display can be controlled and an imagecan be produced. The light emitted from each of the areas thus becomesall or part of a picture element or “pixel.” For a general overview ofFED technology, see D. A. Cathey, Jr., “Field Emission Displays,”Information Display Vol. 11, No. 10, pp, 16-60, October 1995,incorporated herein by reference in its entirety).

The manufacture of a FED presents several technical challenges. Forexample, application of phosphor to a conductive surface may involve theuse of photoresist masks, as described in, for example, U.S. Pat. No.4,891,110 to Libman, et al., which patent is incorporated herein in itsentirety by reference. The use of this photoresist mask may cause someproblems. As described in Libman et al., the photoresist is fixed incertain areas over a conductive surface, the unfixed photoresist is thenremoved by a wash (using, for example, water) and the exposed conductivesurface is subjected to a cataphoretic bath to apply a phosphor to theconductive surface. After that application, the fixed photoresistmaterial must be removed, which is accomplished in the field emissiondisplay art by way of washing with, for example, a hydrogen peroxidesolution. Such washing involves mechanical agitation, which can dislodgeparticles of phosphor, resulting in unacceptable displays. This qualityproblem becomes even more critical as phosphor spot size or line widthshrinks to achieve higher resolutions products.

To provide contrast in ambient light, a dark matrix material may beplaced in the interstitial regions between the phosphor pixels.Unfortunately, many potential matrix materials have significantdisadvantages when utilized under conditions associated with themanufacture of an FED. For example, di-aqueous graphite (DAG) tends toburn when heated in the presence of oxygen. Furthermore, DAG isconveniently used only in a bake-on/lift-off process, which is notfeasible for use in the manufacture of high resolution or small areaFEDs. Manganese carbonate, which is light in color upon initial depositonto a display, tends to turn brown when subjected to elevatedtemperature under vacuum conditions (see Libman et al.). Such browningof manganese carbonate adversely effects contrast of the FED.

Accordingly, there is a need for a method and system for manufacture offield emission displays that will not mechanically agitate the phosphorduring removal of photoresist material. Furthermore, there is a need inthe art for a matrix material which remains black after being subjectedto conditions associated with FED manufacture, particularly at elevatedtemperatures under vacuum. There is also a need for a black matrixmaterial which may be applied by deposit techniques suitable for FEDmanufacture. The present invention fulfills these needs and providesfurther related advantages.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a method isprovided for producing high resolution displays. In brief, the presentinvention is directed to a black matrix material for adherence to theinterstitial regions between light-emitting phosphor pixels of a fieldemission display. The black matrix material is selected from boroncarbide, silicon carbide, tungsten carbide, vanadium carbide, andmixtures thereof. Such materials remain black when subjected to FEDmanufacturing conditions, and are both chemically inert and stable,making them particularly well suited within the practice of thisinvention.

In one embodiment of this invention, a method for manufacturing afaceplate for an FED is disclosed. The method involves depositing,preferably electrophoretically, the black matrix material on at least aportion of the faceplate. Prior to deposit, the faceplate may bepatterned with a photoresist to expose only those areas of the faceplateon which the black matrix material is to be deposited. After depositingthe black matrix material, the photoresist may be removed. A newphotoresist is then patterned to expose only those areas of thefaceplate on which the phosphor is to be deposited, followed bydepositing phosphor in those exposed areas. After deposit of the blackmatrix material and phosphor, an appropriate binder may be employed,followed by successive baking steps. The resulting faceplate may then beused in the assembly of an FED.

In another embodiment, a method is disclosed for depositing a blackgrille on a faceplate of an FED by contacting the faceplate with anelectrophoresis solution containing the black matrix material, andelectrophoretically depositing the black matrix material on at least aportion of the faceplate. In this embodiment, the faceplate may again bepatterned with a suitable photoresist prior to deposition of the blackmatrix material.

In another embodiment, a composition for electrophoretically depositinga black grille on a faceplate is disclosed, wherein the compositioncomprises the black matrix material, and preferably one or more of anelectrolyte, an anti-agglomerating agent and a solvent.

In still a further embodiment, a faceplate having a black matrixmaterial deposited thereon, as well as an FED comprising such afaceplate, are disclosed. Also disclosed are faceplates and FEDs madeaccording to the above methods.

In yet another embodiment, a screen is disclosed. The screen comprises asubstrate; a conductive layer carried by said substrate and covering aportion of said substrate; and a cathodoluminescent layer carried bysaid substrate and overlaying a region of said conductive layer. Thecathodoluminescent layer includes: a first region defining a pluralityof non-contiguous sub-regions, and a second region interstitial saidsub-regions; said first region comprising light emissive substance andsaid second region comprising black matrix material.

Another embodiment of the invention provides for a field emissiondisplay. The field emission display comprises: an extraction grid havinga plurality of openings; an emitter substrate including a plurality ofemitters aligned with said plurality of openings; and a screen adjacentsaid extraction grid. The screen comprises: a substrate; a conductivelayer carried by said substrate and covering a portion of saidsubstrate; and a cathodoluminescent layer carried by said substrate andoverlaying a region of said conductive layer. The cathodoluminescentlayer comprises: a first region defining a plurality of non-contiguoussub-regions, and a second region interstitial said sub-regions; saidfirst region comprising light emissive material and said second regioncomprising black matrix material; said sub-regions aligned to respectiveemitters.

In another embodiment of the invention, there is provided a displaydevice. The display device comprises: a video signal generator capableof generating an image signal (e.g., a television or camcorder); anelectronic controller driven by an image signal from said video signalgenerator, said electronic controller controlling an array of emittercontrol circuits; an emitter substrate including an array of emitters,said emitter control circuits individually coupled to individualemitters; an extraction grid having a plurality of openings, saidopenings aligned with said array of emitters; and a screen adjacent saidextraction grid. The screen comprises a substrate; a conductive layercarried by said substrate and covering a portion of said substrate; anda cathodoluminescent layer carried by said substrate and overlaying aregion of said conductive layer. The cathodoluminescent layer includes:a first region defining a plurality of non-contiguous sub-regions, and asecond region interstitial said sub-regions; said first regioncomprising phosphor pixels and said second region comprising blackmatrix material.

These and other aspects of this invention will become apparent uponreference to the attached figure and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and forfurther advantages thereof, reference is made to the following DetailedDescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a sectional, side elevation, diagrammatic view of anembodiment of the present invention near the start of processing.

FIG. 2 is a sectional, side elevation, diagrammatic view of theembodiment of FIG. 1 at a further stage of processing.

FIG. 3 is a sectional, side elevation, diagrammatic view of acataphoretic deposition device useful according to one exampleembodiment of the present invention.

FIG. 4 is a flow chart of a process provided according to one aspect ofthe present invention.

FIGS. 5A and 5B are sectional, side elevation, diagrammatic views of theembodiment of the present invention in a still further stage ofprocessing.

FIGS. 6A to 6C are sectional, side elevation, diagrammatic views of anembodiment of the present invention for forming the grille.

FIG. 7 is a sectional, side elevation, diagrammatic view of anothercataphoretic deposition device useful with the embodiment of the FIGS.6A to 6C.

FIG. 8 is a cross-sectional view of a representative FED faceplate ofthis invention illustrating the location of the black matrix material inrelation to the phosphor pixels, conductive layer and faceplatesubstrate.

FIG. 9 is a block diagram of a portion of a field emission displayaccording to the preferred embodiment of the invention showing a groupof three emitters controlled by respective column and row drivercircuits.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, an embodiment of the present invention will bedescribed in which a method for producing high resolution displays isprovided. The method comprises forming a faceplate 10 by: depositing anelectrically conductive coating (to provide an electrically conductivelayer) 12 over a screening surface 14; shielding the electricallyconductive coating/layer 12 with a grille 16 formed of black matrixmaterial and having a set of holes 18 formed therein exposing a matrixof areas 20 on the electrically conductive coating/layer 12. The grillemay be formed in much the same manner as a phosphor coating, namely,coating with a resist, soft baking, exposing, developing, and depositingthe grille material. According to alternate embodiments, non-conductivecoatings are used. Also, according to another embodiment, no suchconductive layer is used, and a grille is applied directly to a screen(also referred to as the substrate). As used herein, the term “screenlayer” defines either the screen or a layer applied to the screen, suchas electrically conductive coating 12.

Referring now to FIG. 2, the process further comprises applying a layer22 of insulative photoresist to the grille 16 and the areas 20 ofelectrically conductive coating/layer 12 exposed by the grille; fixingsets of areas 24G and 24B of photoresist-covered areas, whereby fixedsets of area 24G and 24B and an unfixed set of areas 24R are defined.According to the embodiment shown, the fixing is accomplished by shiningultraviolet light 26 through a mask 28, which is similar to asemiconductor lithography mask. These masks may be made of quartz (orglass) and have opaque layer 29 on them (such as chrome oxide or blackchrome) to set a pattern, as is known to those skilled in the art.Alternative methods of fixing include the use of a positive photoresist,where the fixing comprises application of the photoresist and light isapplied to the areas where it is desired that the photoresist beunfixed.

Referring now to FIG. 3, the process further comprises: removing thephotoresist from the unfixed set; and depositing a light-emittingsubstance 30R on the exposed-conductive area. According to oneembodiment, the depositing is accomplished through cataphoreticdeposition as known to those of skill in the art. The illustrated tank32 is filled with an appropriate electrolyte 34 and contains anelectrode 36 connected to a power supply 38, which is also connected tothe electrode of the faceplate 10.

According to a more specific embodiment, the light-emitting substance30R comprises a phosphor, which may be one or more of the following:zinc silicate-manganese; zinc sulphide-copper; zinc berylliumsilicate-manganese; zinc sulphide-silver and zinc cadmiumsulphide-silver; calcium tungstate; zinc sulphide-silver and zinccadmium sulphide-copper; calcium pyrophosphate; potassium chloride (darktrace-nonluminescent—called a Scotophor); zinc sulphide-silver; zincmagnesium fluoride-manganese; magnesium silicate-manganese; zinc oxide;calcium magnesium silicate-cerium; zinc oxide and zinc cadmiumsulphide-copper; calcium magnesium silicate-titanium and calciumberyllium silicate-manganese; potassium magnesium fluoride-manganese;zinc cadmium sulphide-silver; magnesium fluoride-manganese; zincsulphide-silver, zinc silicate-manganese, zinc phosphate-manganese; zincsulphide-silver, zinc cadmium sulphide-cadmium sulphide-silver; zincsulphide-silver, zinc cadmium sulphide-vanadate-europium; zincsulphide-silver, zinc cadmium sulphide-oxysulphide-europium; zincsulphide-silver, zinc cadmium sulphide-oxide-europium; zincsulphide-silver, zinc cadmium sulphide-copper; yttriumoxysulphide-europium; zinc oxide; calcium silicate-lead-manganese; zincphosphate-manganese; zinc cadmium sulphide-copper; zinc sulphide-copper;calcium magnesium silicate-titanium zinc cadmium sulphide-copper; zincsulphide-lead-copper; zinc sulphide selenite-silver; zincsulphide-silver-nickel; zinc cadmium sulphide-silver-nickel; zincmagnesium fluoride-manganese; zinc silicate manganese-arsenic; zincsulphide-silver zinc cadmium sulphide-copper; zinc magnesiumfluoride-manganese calcium magnesium; silicate-cerium; zincsulphide-copper-zinc silicate-manganese-arsenic; gadoliniumoxysulphide-terbium; lanthanum oxysulphide-terbium; yttriumoxysulphide-terbium; yttrium aluminate-cerium; yttrium silicate-cerium;Penetron phosphor/yttrium vanadate-europium (Red) (10 KeV), zincsilicate-manganese (green) (17 keV); Penetron phosphor—red @ 8 keV,green @ 15 keV; Penetron phosphor—red @ 6 keV, green @ 12 keV; zincsilicate-titanium; yttrium gallium aluminum garnet-terbium; yttriumoxysulphide-terbium zinc cadmium sulphide-copper; zinc sulphide-silver;and yttrium oxide-europium.

It is fully within the scope of the present invention to apply a bindermaterial to the substrate in order to firmly attach the light emittingsubstance, e.g., phosphor, and grille material to the substrate. Asuitable binder would be a 1% by weight solution of an organo-silicate,such as TECHNIGLAS GR650F, in isopropanol or other suitable solvent.This could be applied by a puddle or spray application, or othersuitable method, with the substrate then being spun dry at approximately1000 RPM.

It would also be within the scope of the invention to eliminate theorganic materials (which could include the binder or components thereof)from the screen/substrate. These organic materials may be eliminated bya baking operation. If the organic materials are not baked out, thenthere may be problems with carbon contamination which could adverselyaffect the future performance of the phosphor. The preferred bakingwould be done in a suitable oven ramped to 650-700° C. at a rate thesubstrate can handle without breaking. The parts need be held attemperature for only about 10 minutes to 3 hours, preferably about 30minutes in order to eliminate substantially all of the organicmaterials, and thereafter are cooled and removed from the oven.

Referring now to FIG. 4, which shows the process flow in block diagramform, the process further comprises plasma etching the fixed set 24G and24B of insulative photoresist. Examples of acceptable etchers includeeither barrel type or parallel plate etchers, as are known by thoseskilled in the art.

Referring now to FIGS. 5A and 5B, the method further comprises applyinga layer 40 of insulative photoresist (for example, an OCG SC seriesphotoresist) to the entire substrate and fixing the photoresist in allareas except 24B of the insulative photoresist covering theexposed-conductive area 20. Using, for example, a gentle wash withdeveloper appropriate for photoresist, the unfixed portion of theinsulative photoresist covering is then removed, and a second colorlight emitting substance 30B is deposited on the exposed-conductivearea, as discussed above with respect to the first color light emittingsubstance. Acceptable techniques for applying layer 40 include, forexample, meniscus coating, spin coating, curtain coating, and othermethods that will occur to those skilled in the art such as cataphoreticdeposition. Phosphors useful with various means of application will beunderstood by those of skill in the art from the present description.

Referring now to FIGS. 6A-6C, an acceptable method for forming grilles,having a patterned array of holes therein, will be described. Accordingto this method, the forming comprises: applying a layer 42 of insulativephotoresist to the electrically conductive coating/layer 12; fixing oneset 44 of photoresist-covered conductive areas; and removing the unfixedphotoresist with, for example, a gentle wash with developer appropriatefor the photoresist used (for example, Waycoat Negative PhotoresistDeveloper for SC resists made by OCG).

Referring now to FIG. 7, the faceplate 10 is subjected to a cataphoreticbath 46, wherein a potential is developed between the conductivecoating/layer 12 and electrode 48, which comprises, in this example,stainless steel. As a result, the grille 52 forms on the conductivecoating/layer (it may also be referred to as a “surface”) 12 where theunfixed photoresist was removed. The fluid used in the cataphoretic bath46 comprises, for example, about 99.7% by weight of vehicle (forexample, isopropyl alcohol) no more than 0.02% by weight electrolyte(for example, lanthanum nitrate hexahydrate), about 0.05 to 0.10% byweight glycerol, and a powder phosphor or a light-absorbing (alsoreferred to as “black matrix”) material. Up to 1% water can be added tothe phosphor or light absorbing material.

Thus, by the methodology described above, and by methodology describedbelow in connection with FIG. 8, the present invention provides a blackmatrix material for adherence to the interstitial regions betweenlight-emitting pixels of a faceplate. The preferred black matrixmaterial of this invention is black when deposited on the faceplate, anddoes not require subsequent heating to render it opaque. Moreover, whenthe black matrix material of this invention is subjected to processconditions associated with FED manufacture (including heat cycles undervarious atmospheres and vacuum), the matrix material does not changecolor. The black matrix material of the present invention is chemicallyinert and remains stable in vacuum conditions under electronbombardment, and thus does not outgas or chemically decompose during FEDmanufacture. Furthermore, the black matrix material functions as a blackbody by absorbing all wavelengths (particularly the visible spectrum) ofincident radiant energy. Thus, the black matrix material providesexcellent contrast by not reflecting incident light in the visiblerange. The black matrix material may also be referred to as alight-absorbing material, and may serve to block light emitted from afirst of adjacent pixels from reaching a second of adjacent pixels.

Referring now to FIG. 8, a representative FED faceplate 60 of thisinvention is depicted. Black matrix material 62 (indicating symbolicallyby the stippling) is located within the interstitial regions between thelight emitting substance (e.g., phosphor pixels) 64. Both the blackmatrix material and the pixels are in contact with conductivecoating/layer 66, which in turn is in contact with faceplate substrate68. The conductive coating/layer may be indium-tin oxide or tin oxide,and the faceplate substrate may be glass, or maybe formed of thematerials disclosed above. The pixels may be formed of phosphormaterials such as those disclosed above. It will be understood by oneskilled in this field that the pixels may be arranged in any number ofpatterns on the faceplate, and that pixels of multiple colors (e.g., atriad of red, green and blue) may be employed to generate color images.The black matrix material located between the pixels collectively formsthe “grille”, and the term black matrix material is used hereininterchangeably with the terms grille material and light-absorbingmaterial.

Suitable black matrix materials for this invention include, withoutlimitation, manganese carbonate, cobalt oxide black, iron oxides mixedwith cobalt oxides, boron carbide, lead (IV) oxide, niobium (II) oxide,niobium (IV) oxide, palladium (II) oxide, rhenium (IV) oxide, tungstencarbide, silicon carbide, vanadium carbide, copper oxide, boronsilicide, chrome (II) oxide, germanium oxide, iridium oxide, titaniumoxide, manganese carbide, manganese phosphide, manganese tantalate,osmium oxide, strontium boride, strontium carbide, thorium silicide,molybdenum (II) oxide, molybdenum (III) oxide, molybdenum sulfide, andpraseodymium manganese oxide. Boron carbide, titanium carbide, siliconcarbide, vanadium carbide and mixtures thereof are preferred blackmatrix materials. In a preferred embodiment, the black matrix materialis vanadium carbide. Such material is commercially available in the formof a fine powder from a number of suppliers, such as Aldrich ChemicalCo., Inc. (Milwaukee, Wis.) and Alfa Aesar (Bologna, Italy).

Particles of black matrix material having a diameter of about threemicrons or less generally do not require milling before use (asdisclosed in further detail below). However, particles larger than aboutthree microns are preferably milled to a smaller particle size, orseparated and removed from the powdered material prior to use. The blackmatrix material may then be formulated in an appropriate manner fordepositing the same in the interstitial regions between thelight-emitting phosphor pixels of the FED faceplate by, for example,cataphoretic bath as described above or other electrophoretic process,screen printing, dusting or a slurry method.

In the case of high resolution FEDs, and FEDs of small surface area, theblack matrix material is preferably deposited electrophoretically. Inthis embodiment, an electrophoresis solution is made containing theblack matrix material, and preferably also contains one or more of anelectrolyte, an anti-agglomerating agent and a solvent. A suitablesuspension may contain from about 0.03-1.0 wt % of the black matrixmaterial (powdered form), about 0.001-0.2 wt %, preferably about 0.02 wt% of the electrolyte, from about 0.03 to 1.0 wt % of theanti-agglomerating agent, and solvent (also referred to as vehicle).Water may optionally be present up to about 2 wt % to favorably modifythe deposition parameters and/or deposited layer quality. This solutionmay then be utilized to deposit the black matrix material usingconventional electrophoresis techniques, such as that disclosed in U.S.Pat. No. 4,891,110 (which is incorporated herein by reference in itsentirety). In this context, suitable electrolytes include (but are notlimited to) lanthanum nitrate hexahydrate, magnesium nitratehexahydrate, aluminum nitrate nonahydrate, thorium nitrate dodecahydrateand cerium nitrate hexahydrate and indium nitrate pentahydrate.Anti-agglomerating agents include (but are not limited to) glycerol andother polyhydric alcohols. Suitable solvents include (but are notlimited to) organic solvents such as alcohols and ketones. Solvents withdielectric constants between 12 and 25 are generally most suitable, andisopropanol is a preferred solvent.

In manufacturing an FED utilizing the black matrix material of thisinvention, the FED faceplate is preferably patterned with photoresist,leaving open areas where the black matrix material is to be deposited.Suitable photoresists, as well as methods for coating, softbaking,exposing (to pattern the areas for deposit of black matrix material),and developing have been described above and/or are well known to thoseskilled in this field. The patterned photoresist layer must beinsulative and compatible with subsequent processing. For example, theelectrophoresis method for depositing the black matrix material withinthe openings formed by the photoresist has two major steps: 1) particletransport to the cathode, and 2) electrochemical reaction of electrolyteat the cathode. The electrochemical reaction fixes the black matrixmaterial to the substrate, and only occurs on parts of the substratewhich are exposed to the solution and in electrical contact with thecircuit. Therefore the resist has to cover areas not to be coated, andprovide a cover that has sufficient insulation to prevent theelectrochemical reaction from taking place. The resist must becompatible with subsequent processing, so that it will not react ordissolve in the electrophoretic bath, and it must not fail under theelectric potential generated by the electrophoresis reaction.

The voltage applied for electrophoresis is between about 100 volts andabout 200 volts, with a current at about 0.01×10⁻³ amperes per squarecentimeter. The specific resistance of the bath is between about 5×10⁵and about 1.0×10⁶ ohms per centimeter. The application of insulativegrilles in the above-described manner provides for holes in the fixedset of photoresist-covered conductive areas.

After deposit of the black matrix material, the photoresist may beremoved by known techniques, and the process repeated to deposit thephosphor. More specifically, the photoresist is stripped, and then thefaceplate having the black matrix material deposited thereon is againcoated with photoresist, softbaked, exposed (to pattern the areas forphosphor deposit), and developed. The phosphor is then deposited withinthe open areas of the photoresist by, for example, electrophoresis,resulting in a faceplate having phosphor pixels and a black matrixmaterial in the interstitial regions between the pixels.

A preferred subsequent treatment of the FED faceplate includesapplication of an appropriate binder to the black matrix material andphosphor. Suitable binders in this regard include (but are not limitedto) organo-silicates, colloidal silica and silicates. Theorgano-silicate binder will subsequently need to be baked at hightemperatures to remove the carbon, as discussed above. For FEDfaceplates which cannot readily tolerate these high baking temperatures,it is preferred to use the colloidal silica and silicates as the binder,as they cure at essentially room temperature.

Next, photoresist may be removed by plasma etching, conducted as isknown to those of skill in the art. However, according to some specificembodiments of the invention, the photoresist used should be chosen suchthat it does not leave a residual ash after plasma etching. Thefollowing are believed or known to be acceptable: polyisoprene basedphotoresists, polyvinyl alcohol-based photoresists, some polyimide basedresists and some negative chemically amplified resists.

During the plasma etching, it is acceptable to use a pressure of about 1Torr, power of between about 400 to about 500 watts, in a gas atmosphereof: air, oxygen/nitrogen mixture, or any other suitable gases forstripping the photoresist. Other examples known or believed to beeffective include oxygen and hydrogen/argon mixtures.

Process time during the etch is, according to some embodiments, about 30minutes, but this time varies depending upon etch process parameters andthe particular photoresist used. It will be recognized that changes maybe made in the above-described example embodiments without departingfrom the spirit and scope of the present invention.

A flat panel display may be prepared from the faceplate(s) of theinvention described above. As shown in FIG. 9, a display device 70,which may be a television, computer display, or similar device, includesan electronic controller 72 driven by an image signal V_(IM) from avideo signal generator 74. The video signal generator 74 may be, forexample, a television receiver, a computer, a camcorder, a VCR, etc. Inresponse to the image signal V_(IM) the controller 72 controls an arrayof emitter current control circuits 76, each coupled to a respectiveemitter 78. Although a single emitter 78 is coupled to each emittercontrol circuit 76 in FIG. 9, it will be understood that the emitter 78may represent a set of commonly connected emitters. The current througheach emitter 78 can be controlled independently, because a separatecontrol circuit 76 couples to each emitter 78. While the array isrepresented by only three control circuits 76 and emitters 78 forclarity of presentation, it will be understood that typical arraysinclude several hundred control circuits 76 and sets of emitters 78arranged in rows and columns.

The emitters 78 are aligned with respective openings in an extractiongrid 80 adjacent a screen 82. The extraction grid 80 is a conventionalextraction grid formed as a planar conductor having several holes, eachaligned with a respective emitter 78. The screen 82 is a conventionalscreen formed from a glass plate 84 coated with a transparent,conductive anode 86 which is coated, in turn, by a cathodoluminescentlayer 88. The cathodoluminescent layer 88 is formed from a first regiondefining a plurality of non-contiguous sub-regions 87, and a secondregion 89 interstitial (i.e., between, surrounding, covering the areasbetween) the sub-regions 87. The sub-regions (and hence the firstregion) comprises a light emissive substance/material (e.g., phosphor),while the second region comprises black matrix material, i.e., forms thegrille as described herein.

During typical operation, the extraction grid 80 is biased toapproximately 30-100 V and the anode 86 is biased to approximately 1-2kV. A row driver 94 and column driver 96 within the controller 72activate selected ones of the emitters 78 by selectively controlling therespective control circuits 76 through row lines 90 and column lines 92.The control circuits 76 activate the emitters 78 by connecting theemitters 78 to a bias voltage or ground which allows electrons to flowto the emitters 78. The extraction grid 80 extracts the providedelectrons by creating a strong electric field between the extractiongrid 80 and the emitter 78. In response, the emitter 78 emits electronsthat are attracted by the conductive coating/layer 86. The electronstravel toward the layer 86 and strike the cathodoluminescent layer 88,causing light emission at the impact site. Because the intensity of theemitted light corresponds in part to the number of electrons strikingthe cathodoluminescent layer 88 during a given activation interval, theintensity of light can be controlled by controlling electron flow to theemitters 78.

The invention thus provides a screen comprising: a substrate; aconductive layer carried by said substrate and covering a portion ofsaid substrate; and a cathodoluminescent layer carried by said substrateand overlaying a region of said conductive layer; where saidcathodoluminescent layer includes: a first region defining a pluralityof non-contiguous sub-regions, and a second region interstitial saidsub-regions; said first region comprising light emissive substance andsaid second region comprising black matrix material.

The invention additionally provides a field emission display comprising:an extraction grid having a plurality of openings; an emitter substrateincluding a plurality of emitters aligned with said plurality ofopenings; a screen adjacent said extraction grid, said screencomprising: a substrate; a conductive layer carried by said substrateand covering a portion of said substrate; and a cathodoluminescent layercarried by said substrate and overlaying a region of said conductivelayer; said cathodoluminescent layer comprising: a first region defininga plurality of non-contiguous sub-regions, and a second regioninterstitial said sub-regions; said first region comprising lightemissive material and said second region comprising black matrixmaterial; said sub-regions aligned to respective emitters.

According to another embodiment of the invention, a display device isprovided, where the display device comprises: a video signal generatorcapable of generating an image signal; an electronic controller drivenby an image signal from said video signal generator, said electroniccontroller controlling an array of emitter control circuits; an emittersubstrate including an array of emitters, said emitter control circuitsindividually coupled to individual emitters; an extraction grid having aplurality of openings, said openings aligned with said array ofemitters; a screen adjacent said extraction grid, said screencomprising: a substrate; a conductive layer carried by said substrateand covering a portion of said substrate; and a cathodoluminescent layercarried by said substrate and overlaying a region of said conductivelayer; said cathodoluminescent layer including: a first region defininga plurality of non-contiguous sub-regions, and a second regioninterstitial said sub-regions; said first region comprising phosphorpixels and said second region comprising black matrix material.

According to another embodiment of the present invention, a method isprovided for producing high resolution displays, the method comprising:depositing an electrically conductive coating over a screening surface;shielding the electrically conductive coating with a grille having a setof holes formed therein exposing a set of areas of the electricallyconductive coating; applying a layer of insulative photoresist to thegrille and the exposed areas of electrically conductive coating, wherebya plurality of photoresist-covered conductive areas are defined; fixingone set of the plurality of photoresist-covered conductive areas,whereby a fixed set is defined, and an unfixed set is defined; removingthe photoresist from the unfixed set; depositing a light emittingsubstance on the exposed-conductive area; and plasma etching the fixedset of insulative photoresist.

According to a further embodiment of the invention, a system forproducing high resolution displays is also provided. The systemcomprising: depositor of an electrically conductive coating over ascreening surface; depositor of a grille having a set of holes formedtherein applied to the screening surface; depositor of a grille having aset of holes formed therein applied to the screening surface andexposing a set of areas of the electrically conductive coating;applicator of a layer of insulative photoresist to the grille and theexposed areas of electrically conductive coating, whereby a plurality ofphotoresist-covered conductive areas are defined; fixer of one set ofthe plurality of photoresist-covered conductive areas, whereby a fixedset is defined, and an unfixed set is defined; remover of thephotoresist from the unfixed set; depositor of a light emittingsubstance on the exposed-conductive area; and plasma etcher of the fixedset of insulative photoresist.

According to another embodiment of the invention, a method (“Method 1”)is provided for producing high resolution displays. Method 1 comprisesthe steps of: applying a grille to a screen layer, the grille having aset of holes formed therein exposing an exposed set of areas of thescreen layer; applying a layer of photoresist to the grille and theexposed areas of the screen layer, whereby a plurality ofphotoresist-covered screen layer areas are defined; fixing one set ofthe plurality of photoresist-covered screen layer areas, whereby a fixedset is defined, and an unfixed set is defined; removing the photoresistfrom the unfixed set; depositing a light emitting substance on theexposed areas of the screen layer; and plasma etching the fixed set ofphotoresist.

Preferably, Method 1 further comprises depositing an electricallyconductive coating over a screening surface (to provide Method 2).Preferably, said plasma etching of the photoresist to define anexposed-conductive area (as set forth in Method 2), and said depositinga light emitting substance on the exposed-conductive area (as also setforth in Method 2) comprises depositing a first color light emittingsubstance and defining a first deposit area, the method furthercomprising: applying a layer of photoresist to the exposed-conductivearea and the entire substrate; fixing the photoresist everywhere exceptwhere phosphor is to be deposited; removing the unfixed portion of thephotoresist covering; and depositing a second color light emittingsubstance on the exposed-conductive area (so as to provide Method 3).Preferably, said fixing one set according to Method 3 comprises:exposing all areas of the photoresist-covered conductive areas that arenot to be deposited on to light (so as to provide Method 4). Preferably,said exposing of Method 4 comprises: shining light through a mask (so asto provide Method 5). Preferably, said exposing of Method 5 comprises:generating ultraviolet light from a light source; and passing theultraviolet light through the mask wherein light passing through themask impinges upon the set of the plurality of photoresist-coveredconductive areas (so as to provide Method 6). Preferably, Method 3further comprises etching the fixed photoresist (so as to provide Method7). Preferably, said depositing the light emitting substance on theexposed areas of the screen according to Method 1 comprises:cataphoretic deposition (so as to provide Method 8). Preferably, saidremoving the photoresist from the unfixed set according to Method 1comprises: rinsing with developer. Preferably, said light emittingsubstance of Method 1 comprises phosphor.

According to another embodiment of the invention, a system (System 11)is provided for producing high resolution displays. System 11 comprises:a depositor of a grille having a set of holes formed therein applied tothe screening surface that exposes a first set of exposed areas of thescreening surface; an applicator of a layer of photoresist to the grilleand the first set of exposed areas of the screening surface, whereby aplurality of photoresist-covered screening surface areas are defined; afixer of one set of the plurality of photoresist-covered screeningsurface area, whereby a fixed set of areas is defined, and an unfixedset of areas is defined; a remover of the photoresist from the unfixedset, whereby a second set of exposed areas are defined; and a depositorof a light emitting substance in the second set of exposed areas; and aplasma etcher of the fixed set of photoresist.

Preferably, said depositor of a light emitting substance on the secondset of exposed areas according to System 11 comprises deposition of afirst color light emitting substance that defines a first deposit area,and said plasma etcher of the fixed set according to System 11 definesan exposed-conductive area, and System 11 further comprises: anapplicator of a layer of photoresist to the entire substrate; a fixer ofthose portions of the photoresist covering the areas where deposition isnot wanted; a remover of the unfixed portion of the photoresistcovering; and a depositor of a second color light emitting substance onthe exposed-conductive area (so as to provide System 12). Preferably,the fixer of System 12 comprises a light source (so as to provide System13). Preferably, the light source of System 13 comprises an ultravioletlight source (so as to provide System 14). Preferably, said light sourceof System 14 further comprises: a mask through which the ultravioletlight shines onto a portion of the photoresist to be fixed (so as toprovide System 15). Preferably, said depositor of a light emittingsubstance on the exposed-conductive area of System 12 comprises: acataphoretic bath (so as to provide System 16). Preferably, saidcataphoretic bath of System 16 comprises: a voltage source connectedbetween the conductive coating and an anode, having disposed therebetween an electrolytic fluid; the electrolytic fluid comprising:light-absorptive, non-conductive material, chosen from a groupconsisting of: Manganese carbonate, cobalt oxide black, and iron oxideswith cobalt oxides; and the voltage applied by the voltage source beingbetween about 100 volts and about 600 volts, applied for between about 1minute and about 10 minutes (so as to provide System 17). Preferably,said remover of the photoresist from the unfixed set according to System11 comprises: a developer (so as to provide System 18). Preferably, saidlight emitting substance of System 11 comprises phosphor (so as toprovide System 19).

While the above techniques have been disclosed in the context ofproducing high resolution and/or small surface area FEDs, it should beunderstood that FEDs of lower resolution and/or larger surface area canbe produced using the same or alternative techniques. For example, whiledeposit of the black matrix material and phosphor by electrophoresis ispreferred in the context of high resolution and/or small surface areaFEDs, other techniques may be employed if the FED is not constrained inthis manner. To this end, the phosphor may be deposited by techniquesincluding (but not limited to) slurry settling, dusting, photo-tacky andelectrostatic dusting.

The following examples are offered by way of illustration, notlimitation.

EXAMPLES Example 1 Electrophoresis Solution Containing a Suspension ofBlack Matrix Material

In this example, an electrophoresis solution containing a black matrixmaterial, boron carbide, is disclosed. An electrophoresis solution ismade by combining the following components:

Boron carbide (d50 = 1.5 microns) 0.05 wt % De-ionized water 1.00 wt %Lanthanum nitrate 0.02 wt % Isopropanol 98.93 wt % 

Anticoagulant (e.g., glycerol), which is an optional ingredient, may beadded to, or substituted for, the de-ionized water. When present, theanticoagulant is generally present in an amount of about 1 to about 5times the amount of the solid components in the electrophoresissolution.

Example 2 Deposit of Black Matrix Material on FED Faceplate

This example discloses the electrophoretic deposition of a black matrixmaterial in the manufacture of an FED faceplate.

The electrophoresis solution of Example 1 is contained within anelectrophoretic chamber sized to permit complete immersion of thefaceplate, the faceplate having been patterned with a photoresist. Thechamber is preferably made from electrically non-conductive material,and the electrophoresis solution generally has a conductivity less than2 micromhos/cm. Electrophoresis requires a voltage across a submergedanode and cathode pair to produce deposition. Typically, the faceplateis employed as the cathode and a dummy aluminum or stainless steelelectrode is used for the anode. The anode is similar in size to theelectrode. Typically, 200 volts at 0.1-0.2 mA/cm is applied across thecathode-anode pair for 5-6 minutes to achieve the desired deposition ofthe black matrix material on the exposed surfaces of the faceplate.

Example 3 Preparation of Faceplate and FED

After deposit of the black matrix material, the photoresist is strippedaway. A new photoresist coating is then applied, softbaked, exposed (topattern the faceplate for deposit of the phosphor), and developed. Thephosphor is then deposited by electrophoresis within the exposed areasof the faceplate. This photoresist is subsequently stripped away, and acolloidal silica or silicate binder applied to the black matrix materialand phosphor. The faceplate is then baked at a temperature ranging from650° C. to 700° C. at atmosphere for a period of time ranging from 30minutes to 3 hours, followed by a vacuum bake at a temperature of 500°C. for a period of time ranging from 1 hour to 12 hours. When thisprocess is done for color (i.e., three phosphor) screens, the phosphorsteps occur three times. Each time, a third of the pixels are exposedfor phosphor deposition in the appropriate pattern.

The resulting faceplate is then used in the assembly of an FED. Due tothe black nature of the matrix material, the FED screen has highcontrast between the phosphor pixels. In short, the dark outline aroundeach pixel causes the individual pixels to stand out. In addition, theblack matrix material absorbs ambient light, this reducing glare andreflection of the faceplate, as well as reducing any internalreflections between the FED faceplate and emitter panel.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been disclosed herein for the purposeof illustration, various modifications may be made without deviatingfrom the spirit and scope of the invention. Accordingly, the inventionis not limited except as by the appended claims.

What is claimed is:
 1. A field emission display comprising a baseplatethat includes a plurality of emitters, and a faceplate, the faceplatebeing positioned in parallel with the baseplate with the plurality ofemitters facing the faceplate, the faceplate including a black matrixmaterial selected from the group consisting of boron carbide, siliconcarbide, titanium carbide, vanadium carbide and mixtures thereof.
 2. Thefield emission display of claim 1 wherein the black matrix material isprepared by a method comprising, depositing the black matrixelectrophoretically.
 3. The field emission display of claim 1 whereinthe faceplate is patterned with a photoresist and the black matrixmaterial is deposited within an exposed area of the photoresist.
 4. Thefield emission display of claim 1 wherein the faceplate further includesa phosphor deposited on at least a second portion of the faceplate notdeposited with the black matrix material.
 5. The field emission displayof claim 4 wherein the faceplate is patterned with a photoresist and thephosphor is deposited within an exposed area of the photoresist.
 6. Thefield emission display of claim 4, wherein the faceplate furthercomprises a binding agent applied to the black matrix material and thephosphor.
 7. The field emission display of claim 6 wherein the faceplateis made by a step comprising baking the faceplate.
 8. The field emissiondisplay of claim 7 wherein the faceplate is baked at a temperatureranging from 650° C. to 700° C. at atmosphere for a period of timeranging from 10 minutes to 3 hours.
 9. The field emission display ofclaim 7 wherein the faceplate is baked at a temperature of about 500° C.under vacuum for a period of time ranging from 1-12 hours.
 10. The fieldemission display of claim 7, wherein the faceplate is made by a stepcomprising assembling the field emission display incorporating thefaceplate.
 11. A field emission display having a baseplate that includesa plurality of emitters, and a faceplate, the faceplate being positionedin parallel with the baseplate with plurality of emitters facing thefaceplate, the faceplate including a black matrix material selected fromthe group consisting of boron carbide, silicon carbide, titaniumcarbide, vanadium carbide and mixtures thereof, the faceplate being madefrom a transparent plate having the black matrix material deposited onat least a portion thereof.
 12. The field emission display of claim 11wherein the transparent plate is patterned with a photoresist such thatthe black matrix material is deposited on the transparent plate withinan exposed area of the photoresist.
 13. The field emission display ofclaim 11 wherein phosphor is deposited on at least a portion of thetransparent plate not deposited with the black matrix material.
 14. Thefield emission display of claim 13 wherein the black matrix material andphosphor are coated with a binder.
 15. The field emission display ofclaim 14 wherein the faceplate is made by a method that includes bakingthe faceplate.
 16. The field emission display of claim 11 wherein theblack matrix material is deposited on the faceplate by a methodcomprising: contacting the transparent plate with an electrophoresissolution comprising the black matrix material and an electrolyte in anamount of about 0.001-0.2 wt %; and electrophoretically depositing theblack matrix material on at least a portion of the transparent plate.17. The field emission display of claim 16 wherein the solution furthercomprises an anti-agglomerating agent in an amount ranging from about0.03 to 1.0 wt %.
 18. The field emission display of claim 16 wherein thesolution further comprises water.
 19. The field emission display ofclaim 18 wherein water is present in the solution in an amount up toabout 2 wt %.
 20. The field emission display of claim 16 wherein theblack matrix is present in an amount ranging from about 0.03 to 1.0 wt%.